Detecting leaks in pipes

ABSTRACT

An apparatus for permanently or semi-permanently fitting to an underground water pipe  15, 16  for detecting leaks therein, comprises a hydrophone  26  mounted to acoustically monitor water flowing along the pipe  15, 16  and means  29  for analysing a parameter of the output signal of the hydrophone  26  and for generating an alarm signal, in the event that the parameter is above a maximum value or below a minimum value. The apparatus further comprises a radio transmitter for transmitting the alarm signal to a remote receiver, so as to indicate the detection of a leak. The maximum and minimum values are preferably calculated using historical data obtained from the hydrophone  26 , so that the values are automatically adjusted to suit location of the apparatus. In use, a plurality of leak detection apparatus can be installed to pipes at various locations around a geographical area of supply. Once a leak has been identified in an area, it is then a relatively simple matter to more precisely determine where in the area should be surveyed using a conventional leak detector. Thus, the need to survey the whole of the area using a conventional leak detector is avoided.

BACKGROUND OF THE INVENTION

This invention relates to detecting leaks in pipes which carry fluids,such as water.

It is known to locate leaks in underground water pipes using so-calledleak detectors, which can pinpoint leaks prior to excavating the ground.

Before using a leak detector, it is normal to identify the generalgeographic area which is experiencing water loss. Typically, thepresence of a leak is initially identified by taking readings frommeters located at various water distribution points, in order to seewhether there is increased consumption, especially at night.

Suspected leaks can then be located using a leak detector. However, adisadvantage of this arrangement is that it is time consuming tosubsequently survey the whole of the geographical area, in which thereis a suspected fluid loss, using leak localisers.

We have now devised an apparatus for detecting leaks in pipes whichalleviates the above-mentioned problem.

SUMMARY OF THE INVENTION

In accordance with this invention, there is provided an apparatus fordetecting leaks in pipes comprising a transducer for acousticallymonitoring the pipe, means for analysing a parameter of the outputsignal of the transducer and for generating an alarm signal, in theevent that the parameter is above a maximum value or below a minimumvalue, and means for outputting said alarm signal.

In use, a plurality of apparatus in accordance with this invention canbe temporarily or permanently installed to pipes at various locationsaround a geographical area of supply. Thus, once a leak has beenidentified in an area, it is a relatively simple matter to moreprecisely determine where in the area should be surveyed, by monitoringat the remote receiver for an alarm signal. Accordingly, it will beappreciated that the need to survey the whole of the area is avoided.

In one embodiment, the alarm signal output means comprises atransmitter, such as a radio transmitter which transmits a wirelessalarm signal to a remote receiver.

The remote receiver may comprise means for logging the position wherethe alarm signal is received. Thus, for example, receivers may bemounted on delivery vehicles, which frequently drive around areas. Datais then downloaded from the receivers on a regular basis, with theprecise location of any detected alarm signals being recorded.Preferably, the position logging means receives signals from a globalposition satellite.

In a second embodiment, the alarm signal output means may be arranged totransmit the alarm signal along a cable to the remote receiver. In athird embodiment, the alarm signal output means comprises an optical oraudible transducer.

Preferably, the transmitting means transmits a low power radio signal,thereby conserving the battery power of the apparatus and enabling aplurality of apparatus to transmit on the same frequency, without therisk of interference.

In use, an alarm signal can be detected by moving or by driving aroundthe geographical area with a remote receiver unit, until an alarm signalis detected; the point of the leak can then be pinpointed using aconventional leak detector.

Preferably, the transmitter is arranged to transmit a different standbysignal when said parameter is not above said maximum value or below saidminimum value. Thus, it will be apparent that the apparatus may not beworking correctly, when neither the standby signal nor the alarm signalis detected at the remote receiver.

Preferably, the transmitter only transmits a signal periodically, inorder to further conserve battery power.

Preferably, the alarm signal is transmitted more frequently than thestandby signal, so that the alarm signal is less likely to be overlookedwhilst moving or driving around the area.

The most common way of localising leaks is achieved using thecorrelation principle, in which two acoustic transducers are mounted atdifferent points on the pipe under analysis. A correlator then comparesthe noise detected at the two sensor points and determines thedifference between the time which the noise takes to reach one sensorcompared with the time which it takes to reach the other sensor. Thus,the leak position can be determined from the following formula:$L = \frac{D - \left( {V \times T_{d}} \right)}{2}$

where:

L=leak position

D=distance between the sensors

V=velocity of sound for pipe under consideration

T_(d)=time delay between noise signals.

It is difficult and time consuming to attach the acoustic transducers ofa leak localiser to the pipe each time a measurement is taken and itwill be appreciated that it is sometimes necessary to reposition thetransducers and take several new measurements before the leak can bepinpointed.

Thus, preferably, the apparatus comprises a port for providing anexternal connection to its acoustic transducer. In use, once an alarmsignal has been detected by one of the apparatus, the leak can bepinpointed by connecting a correlator to the respective ports of twoleak detection apparatus in accordance with this invention. Thecorrelator then uses the acoustic transducers of the two apparatus totake its measurements and accordingly measurements can be taken far moreeasily and quickly, since no time needs to be spent connecting separateacoustic transducers to the pipe.

Preferably, the port comprises a transmitter which provides a wirelesslink to a corresponding port of the leak localiser. In this manner, theapparatus can be provided with a completely sealed body, so that theingress of fluid can be prevented.

Leaks in pipes generate a noise and this noise can be detected whenthere is a leak. However, a problem of detecting leaks in this manner isthat the noise created by normal fluid consumption can mask the noisecreated by the leak. Thus, preferably, the apparatus comprises a clock,the analysing means being arranged to analyse the parameter of theoutput signal of the transducer at night, when little or no fluidconsumption normally occurs.

All pipes have different noise characteristics from each other. Hence,the noise level indicating a leak will vary greatly throughout thegeographical area. This problem is further exacerbated by the fact thatplastics pipes do not conduct sound as well as metal pipes.

Accordingly, it will be appreciated that it is not possible to reliablydetect for a leak at different locations by merely comparing the valueof the parameter of the output of the transducer at each location withthe same maximum and/or minimum value.

In order to overcome this problem, the analysing means is preferablyarranged to periodically measure the output level of the transducer andto provide an average of previously measured levels, the monitoringmeans being further arranged to determine said maximum and/or minimumvalues from said average. In this manner, the level at which the alarmsignal is triggered at each location is dependent upon the average ofprevious noise values at that location.

Preferably, the alarm signal is also generated, in the event that theparameter is above an absolute maximum value or below an absoluteminimum value.

A disadvantage of using average values to determine the maximum orminimum values is that the readings used in the average calculationcould include readings which are representative of a leak and this couldmean that some leaks go undetected. In order to prevent this, themonitoring means is preferably arranged to reject readings from theaverage calculation which are above a maximum threshold value or below aminimum threshold value.

The maximum and/or minimum threshold values should themselves varybetween locations, in order to take account of the differentsurroundings. Accordingly, the monitoring means is preferably arrangedto reject readings from the average calculation which are apredetermined amount more or less than the median of the storedreadings.

In order to prevent intermittent noise from triggering an alarm, themonitoring means is preferably arranged to only produce an alarm signalif a reading which is above said maximum limit or below said minimumlimit is not substantially different from an adjacent reading.

Preferably, the monitoring means is arranged to take a series ofmeasurements of the output level of the transducer, the monitoring meansbeing arranged to compare the level that has been exceeded for apredetermined percentage number of readings with said maximum or minimumvalues and/or to compare the spread between levels which have exceededpredetermined upper and lower percentage numbers of readings.

Known acoustic transducers can be mounted inside a body which is screwedto a fitting in the pipe. However, a disadvantage of this arrangement isthat air needs to bled out of the body, so that the acoustic transduceris fully in contact with the fluid in the pipe.

Air is carried along with fluid flowing along pipes and this air cancollect in closed cavities in the pipe. Accordingly, a leak detectionapparatus in accordance with this invention may cease to operatecorrectly, unless the cavity in which its transducer is mounted isregularly bled of air.

In one embodiment, an air bleed valve is mounted in a flow passagethrough a body of the apparatus, sensing means being provided foropening said valve, when a build up of air is sensed in the flowpassage.

Alternatively, in accordance with this invention, as seen from a secondaspect, there is provided an assembly comprising a transducer foracoustically monitoring fluid flowing along a pipe, the assemblycomprising a body having a port for connecting to a corresponding portin the wall of the pipe, a fluid-flow passage extending through the bodyand having opposite ends communicating with the port, an acoustictransducer mounted inside the flow passage, and flow diverting means fordiverting at least some of the fluid flowing along the pipe through saidflow passage.

In use, the assembly is attached as a spur to a conventional port in thepipe, with at least some of the fluid in the pipe being branched offthrough the passageway. Thus, the body is continually flushed by thefluid and hence air cannot build up around the transducer. Furthermore,the fluid flushes out any air which is present in the body when theapparatus is first installed.

Preferably, the flow diverting means is arranged to divert all of thefluid flowing along the pipe under analysis through the passageway.

These and other objects, features, and advantages of the presentinvention will be clearly understood through consideration of thefollowing detailed description.

BRIEF DESCRIPTION OF THE DRAWING

An embodiment of this invention will now be described by way of exampleonly and with reference to the accompanying drawing, the single FIGUREof which is a sectional view through a leak detection apparatus, inaccordance with this invention, when connected to a water pipe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawing, there is shown an embodiment of a leakdetection apparatus 10 connected via an adaptor 11 to the body of aconventional stopcock 12 of the kind that is commonly found inunderground pits outside most dwellings. However, it will be appreciatedthat the apparatus could be connected to any convenient point thatallows access to the water in the pipe.

Normally, the stopcock 12 comprises a valve member which can be closedto prevent the flow of water through an aperture 13 in a partition wall14 that is disposed between inlet and outlet pipes 15, 16 connected torespective ports of the stopcock. However, in order to fit the leakdetector 10, the valve member is unscrewed from the body of the stopcock12 and the adaptor 11 fitted in its place. A base 25 of the leakdetector 10 is then screwed to the upper end of the adaptor 11, as shownin the drawing.

The adaptor 11 comprises a tubular extension 17 which seals around theaperture 13 in the partition wall 14. The tubular extension comprises athrough passage 18 which extends through the adaptor 11 and communicateswith a corresponding tubular central passage 19 formed in the base 25 ofthe leak detector 10. A valve member (not shown) may be provided forclosing the through passage 18, so that the stopcock feature is stillprovided.

An annular-section passage 21 extends concentrically with the centralpassage 18 through the adapter 11. The lower end of the passage 21communicates with a chamber 22 formed above the partition wall 14 of thestopcock 14.

The chamber 22 above the partition wall 14 communicates with the inletpipe 15 and a corresponding chamber 23 below the partition wall 14communicates with the outlet pipe 16.

The upper end of the annular-section passage 21 through the adaptor 11communicates with a corresponding annular-section passage 24 in the base25 of the leak detector 10.

An elongate hydrophone 26 is disposed axially within the central passage19 in the base 25 of the leak detector 10. The hydrophone 26 issupported by radially-extending webs (not shown). The upper end of thecentral passage 19 in the base 25 of the leak detector 10 communicateswith the upper end of the outer annular-section passage 24, adjacent abottom wall 27 of a hollow tubular body 28 of the detector.

Wires extend from the hydrophone 26 to a printed circuit board 29sealingly mounted within the body 28 of the leak detector 10. A window30 is provided on the upper end of the body 28 of the leak detector 10and below this is an infra-red transmitter/receiver 31, which isconnected via wires to the printed circuit board 29. A battery (notshown) is also mounted inside the body 28 of the leak detector 10.

In use, once the leak detector and adaptor 11 have been fitted to thestopcock 12, as hereinbefore described, water can be applied to theinlet pipe 15. The water flows from the inlet pipe 15 into the upperchamber 22 of the stopcock 12 and upwardly through the outerannular-section passage 21, 24 in the adaptor 11 and leak detector 10respectively. The water flow then turns radially inwardly and downwardlythrough the central passage 19, 18 in the leak detector 10 and adaptorrespectively, thereby passing the hydrophone 26. Finally, the waterflows into the lower chamber 23 of the stopcock 12 and out into theoutlet pipe 16.

It will be appreciated that the entire water flow is branched off by theadaptor 11 through the leak detector 10 and past the hydrophone 26,which is mounted axially within the passage 19. Accordingly, in use, noair will be able collect around the hydrophone 26 to impede theperformance of the leak detector 10. Furthermore, any air which ispresent in the leak detector when it is initially fitted will be washedaway by the water flow.

Thus, it will be appreciated that the need to bleed the detector of airis avoided, thereby providing the advantage that the detectors requireno further maintenance once they have been installed.

When there is a leak in the pipe, a noise is created as the water flowsthrough the leak. During the daytime, it is difficult to detect thenoise created by a leak, owing to the amount of noise created by normalwater consumption. However, the detector 10 is arranged to acousticallymonitor the pipe at night, when consumption is normally at a minimum.

At night, the increased noise level of a leak can be detected to triggeran alarm. Also, when there is a leak the sound level that is detectedtends to remain substantially level, whereas under no leak the noiselevel fluctuates greatly.

Thus, the detector 10 is arranged to periodically take noise samplesover a predetermined time period, each day during night time hours. Adistribution histogram of noise level against the percentage number ofreadings at those levels is then constructed from the recorded data. Theresults are characterised by level and spread parameters, where:

Level=L_(n1),

Spread=L_(n2)−L_(n3)

The values L_(nx) represent the noise levels that have been exceeded forn% of the time.

Initially, on the first day of installation, a leak is detected bycomparing the two parameters of the readings against respective absolutevalues X and Y, which are preprogrammed into the detector 10. As statedabove, these parameters are the noise level which has been exceeded forn% of the time and the spread between the noise level which has beenexceeded between n2 and n3% of the measurement time.

Thus, a leak is indicated if:

Level (L_(n1))>XdB

or Spread (L_(n2)−L_(n3))<YdB

Over the next six days, a leak is detected by comparing the twoparameters against the absolute values X and Y, as well as to the twoparameters of the readings taken on the first day. In the latter case, aleak is indicated if the present day's parameter is more than apredetermined amount different from the corresponding reading on thefirst day.

After seven days, standard reference values, against which the twoparameters can be compared, are calculated, assuming that no leak hasbeen detected. Initially, the median of the seven days of no leakresults is found for both parameters and the other six values are thencompared with the median.

If the magnitude of the difference between any of the six values and themedian is more than a predetermined amount, then that value is rejectedfrom the reference calculation.

Thus, for example the second level value is rejected if:

|2^(nd) Level−median level|>GdB

Or the second spread value is rejected if:

|2^(nd) Spread−median spread|>HdB

Standard reference values for the two parameters are then formed fromthe average of the values which are not rejected from the referencecalculations.

Each following day, subsequent daily values for level and spread arecompared with the absolute values X and Y as well as with the standardreference values that have been derived.

Thus, a leak is indicated if:

new Level>XdB

or new Spread<YdB

or new Level−Standard level value>QdB

or reference spread value−new spread>RdB

Leaks can be reliably and confidently detected at each apparatuslocation, because the readings at each location are compared withabsolute values, as well as with reference values that are calculatedusing no leak readings, which are taken at that location during thefirst days after installation.

It is possible for noise created by intermittent system use at night tomimic leakage. Thus, once a leak has been detected, the apparatus takesanother set of readings on the same day and determines where these alsoindicate a leak. Accordingly, an alarm condition is only triggered whentwo or more consecutive sets of readings indicate a leak. Obviously,this number can be increased in areas which are prone to intermittentwater usage at night.

When an alarm condition is triggered, a low power radio transmitterhoused inside the body 28 of the apparatus is energised to periodicallytransmit an alarm signal. Under no leak conditions the transmitter maytransmit a periodic standby signal, in order to provide an indicationthat the apparatus is functioning correctly. The mark-to-space ratio ofthe standby signal is preferably larger than the mark-to-space ratio ofthe alarm signal, in order to conserve battery power.

It is envisaged that a plurality of leak detection apparatus inaccordance with this invention will be installed at various locationsaround a geographical area. Thus, when a leak is detected in the area,it is a relatively simple matter to drive around the area with a radioreceiver, until an alarm signal is detected. It will then be apparentthat the leak is adjacent to the point of installation of the apparatuswhich is transmitting the signal.

The leak can then be pinpointed quickly and easily using a leak detectorhaving two remote data acquisition units that are interconnected by awire or by a wireless communication link.

Each unit comprises an optical coupler 50, as shown in the drawings. Inuse, the couplers 50 of the two data logging units are connected torespective leak detection apparatus of the present invention, which arelocated on either side of the suspected leak. The upper end of the body28 of each apparatus extends into a correspondingly-shaped socket 51 inthe coupler 50. An infra-red transmitter/receiver 52 located at theupper end of the socket 51 in the coupler 50 communicates with thetransmitter/receiver 31 in the leak detection apparatus 10, therebyenabling the two logging units to communicate directly with thehydrophones 26 in the respective apparatus with which they areconnected.

The noise generated by the leak is detected by each hydrophone 26,however, the time taken for the noise to reach the two hydrophones isdifferent; the precise location of the leak can accordingly bedetermined as a function of time difference.

While the preferred embodiment of the invention has been shown anddescribed, it will be apparent to those skilled in the art that changesand modifications may be made therein without departing from the spiritof the invention, the scope of which is defined by the appended claims.

I claim:
 1. An apparatus for detecting a leak in a pipe for installationat a location on a pipe, the apparatus comprising: a transducer foracoustically monitoring the pipe; analysing means for analysing aparameter of an output signal of the transducer and for determining if asignal indicating a leak should be outputted; and, signal output meansfor outputting the leak-indicating signal, wherein the analysing meansis configured to determine that said leak-indicating signal should beoutputted in the event that the parameter is below a minimum value andwherein said parameter is the spread of the output levels of saidtransducer and wherein the signal output means is arranged to output astandby signal if the conditions for outputting a signal indicative of aleak are not satisfied.
 2. An apparatus according to claim 1, whereinthe analysing means is configured to determine that said leak-indicatingsignal should be outputted if the spread between the output levels ofthe transducer is below a minimum value and if an output level of thetransducer is above a maximum value.
 3. The apparatus of claim 1,wherein the spread between levels is measured between upper and lowerpredetermined percentage numbers of readings.
 4. The apparatus of claim1, in which the signal output means comprises an optical or audibletransducer.
 5. The apparatus of claim 1, in which the signal outputmeans is arranged to transmit the signal along a cable to a remotereceiver.
 6. The apparatus of claim 1, in which the signal output meanscomprises a transmitter, which transmits a wireless alarm signal to aremote receiver.
 7. The apparatus of claim 6, in which the transmittertransmits a low power radio signal.
 8. The apparatus of claim 1, inwhich the signal output means is arranged to output a standby signal ifthe conditions for outputting a signal indicative of a leak are notsatisfied.
 9. The apparatus of claim 8, in which the signal indicativeof a leak is a signal having a periodic form and the standby signal alsohas a periodic form with a larger period than that of the signalindicating a leak.
 10. The apparatus of claim 1, in which the apparatuscomprises a port for providing an in-situ external connection to theacoustic transducer.
 11. The apparatus of claim 10, in which the portcomprises a transmitter which provides a wireless link to acorresponding port of a leak pinpointer.
 12. The apparatus of claim 1,comprising a clock, the analysing means being arranged to analyse theoutput level of the transducer during night hours.
 13. The apparatus ofclaim 1, in which the analysing means is arranged to periodicallymeasure the output levels of the transducer and provide an average ofpreviously measured levels and being further arranged to determine saidminimum value from said average.
 14. The apparatus of claim 13, in whichthe signal is also generated when the parameter is below an absoluteminimum.
 15. The apparatus of claim 13, in which the analysing means isarranged to reject readings from said average calculation, which areabove a maximum threshold value or below a minimum threshold value. 16.The apparatus of claim 13, in which the analysing means is arranged toreject readings from the average calculation, which are a predeterminedamount more or less than the median of the previously measured levels.17. The apparatus of claim 13, in which the analysing means is arrangedto determine if a signal indicative of an alarm signal should beoutputted in the event that the parameter is below a minimum value andit is not substantially different from an adjacent reading.
 18. Theapparatus of claim 13, wherein the analysing means is configured todetermine that a signal indicative of a leak be outputted if the spreadbetween output levels is below a minimum and the output level of thetransducer is above a maximum and said maximum is also determined froman average of previously measured levels.
 19. The apparatus as claimedin claim 1, in which the analysing means are located at the saidlocation.
 20. The apparatus of claim 1, in which the signal output meansare located at the said location.
 21. The apparatus of claim 1,comprising a body having a port for connecting to a corresponding portin the wall of the pipe, a fluid-flow passage extending through the bodyand having opposite ends communicating with the port, said acoustictransducer mounted inside the flow passage, and flow diverting means fordiverting at least some of the fluid flowing along the pipe through saidflow passage.
 22. An assembly, comprising: a transducer for acousticallymonitoring fluid flowing within a pipe, the assembly comprising a bodyhaving a port for connecting to a corresponding port in the wall of thepipe, a fluid-flow passage extending through the body and havingopposite ends communicating with the port, said acoustic transducermounted inside the flow passage, and flow diverting means for divertingat least some of the fluid flowing along the pipe through said flowpassage.
 23. The assembly as claimed in claim 22, in which the flowdiverting means is arranged to divert all of the fluid flowing along thepipe under analysis through the passageway.
 24. An apparatus fordetecting a leak in a pipe for installation at a location on a pipe, theapparatus comprising: a transducer for acoustically monitoring the pipe;analysing means for analysing a parameter of the output signal of thetransducer and for determining if a signal indicative of a leak shouldbe outputted; and, signal output means adapted to transmit the signalindicative of a leak, wherein the analysing means determines that asignal indicative of a leak be outputted in the event that the parameteris above a maximum value or below a minimum value and wherein theanalysing means is configured to periodically measure the output levelof the transducer and to provide an average of previously measuredlevels, the analysing means being further configured to determine saidmaximum and/or said minimum values from said average.
 25. The apparatusof claim 24, wherein said analysing means is configured to determinethat a signal indicative of a leak should be outputted if the parameteris above a maximum value and where said parameter is the output level ofthe transducer.
 26. The apparatus of claim 24, wherein said analysingmeans is configured to determine that a signal indicative of a leak beoutputted if said parameter is below a minimum value and wherein saidparameter is the spread between output levels of the transducer.
 27. Theapparatus of claim 26, wherein the spread of levels is measured betweenupper and lower predetermined percentage numbers of readings.
 28. Theapparatus of claim 24, in which the signal indicative of a leak isoutputted, in the event that said parameter is above an absolute maximumvalue or below an absolute minimum value.
 29. The apparatus of claim 24,in which said analysing means is arranged to reject readings from saidaverage calculation, which are above a maximum threshold value or belowa minimum threshold value.
 30. The apparatus of claim 24, in which saidanalysing means is configured to reject readings from the averagecalculation, which are a predetermined amount more or less than themedian of the stored readings.
 31. The apparatus of claim 24, in whichsaid analysing means is configured to only produce an alarm signal if areading which is above said maximum limit or below said minimum limit isnot substantially different from an adjacent reading.
 32. The apparatusof claim 24, wherein said analysing means is configured to determinethat a signal indicative of a leak be outputted if the output level ofsaid transducer is above the maximum and if the spread between levels isbelow a minimum.
 33. The apparatus of claim 24, in which the signaloutput means comprises an optical or audible transducer.
 34. Theapparatus of claim 24, in which said signal output means is arranged totransmit the signal along a cable to a remote receiver.
 35. Theapparatus of claim 24, in which said signal output means comprises atransmitter, which transmits a wireless alarm signal to a remotereceiver.
 36. The apparatus of claim 35, in which the transmittertransmits a low power radio signal.
 37. The apparatus of claim 24, inwhich said signal output means is arranged to output a standby signal ifthe conditions for outputting a signal indicative of a leak are notsatisfied.
 38. The apparatus of claim 24, in which said signal outputmeans outputs a periodic signal indicative of a leak when the conditionsfor generating a signal indicative of a leak are satisfied.
 39. Theapparatus of claim 37, in which the signal indicative of a leak is asignal having a periodic form and the standby signal also has a periodicform with a larger period than that of the signal indicating a leak. 40.The apparatus of claim 24, in which the apparatus includes a port forproviding an in-situ external connection to said acoustic transducer.41. The apparatus of claim 40, in which the port comprises a transmitterwhich provides a wireless link to a corresponding port of a leakpinpointer.
 42. The apparatus of claim 24, further including a clock,and said analysing means being arranged to analyse the output level ofsaid transducer during night hours.
 43. An apparatus for detecting aleak in a pipe for installation at a location on a pipe, the apparatuscomprising: a transducer for acoustically monitoring the pipe; analysingmeans for analysing a parameter of the output signal of the transducerand for determining if a signal indicative of a leak should beoutputted; and, a transmitter configured to transmit a signal indicativeof a leak to a remote receiver which is mobile with respect to the pipe,wherein the analysing means is configured to determine that a signalindicative of a leak should be outputted in the event that the parameteris above a maximum value or below a minimum value and wherein saidtransmitter is arranged to transmit a standby signal when said parameteris not above said maximum value or below said minimum value.
 44. Theapparatus of claim 43, in which the signal indicative of a leak is asignal having a periodic form and the standby signal also has a periodicform with a larger period than that of the signal indicative of a leak.45. The apparatus of claim 43, in which the transmitter transmits a lowpower radio signal.
 46. The apparatus of claim 43, further comprisingmeans to identify the said location.
 47. The apparatus of claim 46, inwhich the remote receiver includes means to log the position of thereceiver when it receives the signal indicative of a leak.
 48. Theapparatus of claim 43, in which said transmitter transmits a periodicsignal indicative of a leak.
 49. The apparatus of claim 43, furtherincluding a clock, and said analysing means being arranged to analysethe parameter of the output signal of the transducer during night hours.50. The apparatus of claim 43, in which said said apparatus includes aport for providing an in-situ external connection to the acoustictransducer.
 51. The apparatus of claim 43, in which the port includes atransmitter which provides a wireless link to a corresponding port of aleak pinpointer.
 52. An apparatus for detecting a leak in a pipe forinstallation at a location on a pipe, the apparatus comprising: atransducer for acoustically monitoring the pipe; analysing means foranalysing a parameter of the output signal of the transducer and fordetermining if a signal indicative of a leak should be outputted; and, atransmitter configured to transmit a signal indicative of a leak to aremote receiver which is mobile with respect to the pipe, wherein theanalysing means is configured to determine that a signal indicative of aleak should be outputted in the event that the parameter is above amaximum value or below a minimum value and wherein said analysing meansis arranged to periodically measure the output level of said transducerand to provide an average of previously measured levels and beingfurther arranged to determine said maximum and/or minimum values fromsaid average.
 53. The apparatus of claim 52, in which the signalindicative of a leak is also generated, in the event that said parameteris above an absolute maximum value or below an absolute minimum value.54. The apparatus of claim 52, in which said analysing means is arrangedto reject readings from said average calculation, which are above amaximum threshold value or below a minimum threshold value.
 55. Theapparatus of claim 52, in which said analysing means is arranged toreject readings from the average calculation, which are a predeterminedamount more or less than the median of the previously measured levels.56. The apparatus of claim 52, in which said analysing means is arrangedto only produce an alarm signal if a reading which is above said maximumlimit or below said minimum limit is not substantially different from anadjacent reading.
 57. An apparatus for detecting a leak in a pipe forinstallation at a location on a pipe, the apparatus comprising: atransducer for acoustically monitoring the pipe; analysing means foranalysing a parameter of the output signal of the transducer and fordetermining if a signal indicative of a leak should be outputted; and, atransmitter configured to transmit a signal indicative of a leak to aremote receiver which is mobile with respect to the pipe, wherein theanalysing means is configured to determine that a signal indicative of aleak should be outputted in the event that the parameter is above amaximum value or below a minimum value and, wherein said analysing meansis arranged to take a series of readings of said output level and saidsignal indicative of a leak is generated if said outpput level exceeds apredetermined maximum or if the spread between levels is less than thesaid minimum value and wherein said analysing means is arranged togenerate a signal indicative of an alarm if a predetermined percentageof the readings of the output level exceed the maximum value and if thespread between levels which have exceeded predetermined upper and lowerpercentage numbers of readings are less than the minimum.
 58. Anapparatus for detecting a leak in a pipe for installation at a locationon a pipe, the apparatus comprising: a transducer for acousticallymonitoring the pipe; a port for providing an in-situ external connectionto the transducer, wherein the port includes an infra-red transmitterwhich provides a wireless link to a corresponding port of a leakpinpointer; analysing means for analysing a parameter of the outputsignal of the transducer and for determining if a signal indicative of aleak should be outputted; and, output means configured to output asignal indicative of a leak, wherein the analysing means determines thata signal indicative of a leak should be outputted in the event that theparameter is above a maximum value or below a minimum value.
 59. Anapparatus for detecting a leak in a pipe for installation at a locationon a pipe, the apparatus comprising: a transducer for acousticallymonitoring the pipe; a port for providing an in-situ external connectionto the transducer; analysing means for analysing a parameter of theoutput signal of the transducer and for determining if a signalindicative of a leak should be outputted; and, output means configuredto output a signal indicative of a leak, wherein the analysing meansdetermines that a signal indicative of a leak should be outputted in theevent that the parameter is above a maximum value or below a minimumvalue and wherein said output means is configured to output a standbysignal when said parameter is not above said maximum value or below saidminimum value.
 60. The apparatus of claim 59, in which said signaloutput means comprises an optical or audible transducer.
 61. Theapparatus of claim 59, in which said signal output means is arranged totransmit the signal along a cable to a remote receiver.
 62. Theapparatus of claim 59, in which said signal output means includes atransmitter, which transmits a wireless alarm signal to a remotereceiver.
 63. The apparatus as claimed in 62, in which said transmittertransmits a low power radio signal.
 64. The apparatus of claim 59,further including means to identify the said location.
 65. The apparatusof claim 64, in which a remote receiver includes means to log theposition of the receiver when the receiver receives an alarm signal. 66.The apparatus of claim 59, in which said output means transmits aperiodic signal indicative of a leak.
 67. The apparatus of claim 59, inwhich said signal indicative of a leak is a signal having a periodicform and said standby signal also has a periodic form with a largerperiod than that of said signal indicating a leak.
 68. The apparatus ofclaim 59, further including a clock, and said analysing means beingarranged to analyse the parameter of the output signal of the transducerduring night hours.
 69. The apparatus of claim 59, in which saidanalysing means is arranged to periodically measure the output level ofsaid transducer and to provide an average of previously measured levelsand being further arranged to determine said maximum and/or minimumvalues from said average.
 70. The apparatus of claim 69, in which thesignal indicative of a leak is also generated, in the event that saidparameter is above an absolute maximum value or below an absoluteminimum value.
 71. The apparatus of claim 69, in which said analysingmeans is arranged to reject readings from said average calculation,which are above a maximum threshold value or below a minimum thresholdvalue.
 72. The apparatus as claimed in claim 71, in which said analysingmeans is arranged to reject readings from the average calculation, whichare a predetermined amount more or less than the median of thepreviously measured levels.
 73. The apparatus of claim 69, in which saidanalysing means is arranged to only produce an alarm signal if a readingwhich is above said maximum limit or below said minimum limit is notsubstantially different from an adjacent reading.
 74. The apparatus ofclaim 59, in which the analysing means is arranged to take a series ofreadings of the output level and the signal indicative of a leak isgenerated if the output level exceeds a predetermined maximum or if thespread between levels is less than said minimum value.
 75. The apparatusas claimed in claim 74, in which said analysing means is arranged togenerate a signal indicative of a leak if a predetermined percentage ofthe readings of the output level exceed the maximum value and if thespread between levels which have exceeded predetermined upper and lowerpercentage numbers of readings are less than the minimum.
 76. Theapparatus as claimed in claim 59, in which said analysing means arelocated at the said location. 77.The apparatus of claim 59, in whichsaid signal output means are located at the said location.
 78. Theapparatus of claim 59, further including a body having a port forconnecting to a corresponding port in the wall of said pipe, afluid-flow passage extending through the body and having opposite endscommunicating with the port, said acoustic transducer mounted inside theflow passage, and flow diverting means for diverting at least some ofthe fluid flowing along said pipe through said flow passage.
 79. Theapparatus of claim 59, in which the port includes a transmitter whichprovides a wireless link to a corresponding port of a leak pinpointer.80. The apparatus of claim 79, wherein the wireless link is provided byan infra-red transmitter.
 81. An apparatus for detecting a leak in apipe for installation at a location on a pipe, the apparatus comprisinga transducer for acoustically monitoring the pipe, analysing means foranalysing a parameter of the output signal of the transducer and fordetermining if a signal indicative of a leak or a standby signal shouldbe generated, the signal indicative of a leak being generated if theparameter is above a maximum value or below a minimum value, the standbysignal being generated otherwise, and output means provided at the saidlocation for outputting the required signal.
 82. A system for monitoringa pipe for a leak, the system comprising a plurality of leak detectionunits each being arranged to monitor a section of the pipe for leaks andto transmit a wireless signal, wherein the transmitter transmits asignal indicative of a leak if a leak is detected and a standby signalotherwise, the system further comprising a mobile receiver which isarranged to sequentially receive the wireless signals from the leakdetection units as the receiver moves with respect to the units.
 83. Amethod of monitoring a pipe for leaks, the method comprising the stepsof: providing a plurality of leak detection units at locations on thepipe, each of the detection units being arranged to monitor a section ofthe pipe for leaks and to transmit a wireless signal, wherein thetransmitter transmits a signal indicative of a leak if a leak isdetected and a standby signal otherwise; and, moving a mobile receiverpast the units and sequentially receiving the wireless signal from thenearest unit as the mobile receiver moves into the vicinity of eachunit.
 84. An apparatus for detecting a leak in a pipe for installationat a location on a pipe, the apparatus comprising: a transducer foracoustically monitoring the pipe; analysing means for paralysing aparameter of an output signal of the transducer and for determining if asignal indicative of a leak should be outputted; and a transmitterconfigured to transmit a wireless signal to a remote receiver which ismobile with respect to the pipe, wherein a signal indicative of a leakis outputted if a leak is detected and a standby signal is outputtedotherwise.